Importance of weak interactions in developing 1,3-bis(4,6-dimethyl-1H-nicotinonitrile-1-yl)1,3-dioxy propane polymorphs

The structure of 1,3-bis(4,6-dimethyl-1H-nicotinonitrile-1-yl)1,3-dioxy propane polymorphs has been characterized by X-ray diffraction, FT-IR, 1H and 13C NMR spectroscopies. The influence of intra and intermolecular weak interactions is thoroughly studied in solid state using single crystal X-ray diffraction and FT-IR. These polymorphs belong to monoclinic space group ‘P21/n’ and ‘P21/c’. These polymorphs have C–H⋯n (lone pair), hydrogen bonds, C–N⋯π, C–H⋯π and π⋯π intermolecular non-covalent interactions. These polymorphs are the result of weak interactions and solvent used in crystallization. The FT-IR spectra have been recorded in the solid phase and NMR has been recorded in solvent. The optimized geometry has been calculated by B3LYP methods using different basis sets. The FT-IR and NMR spectra of 1st polymorphs has been calculated at B3LYP/6–31G (d) level. The scaled theoretical wave number showed good agreement with the experimental values. These two polymorphs as well as other stereomers are studied by DFT calculations.

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► Polymorphism: These become important branch in pharmaceutical chemistry due to activity difference in polymorphs.
► Non-covalent interactions: These weak interactions play a vital role to develop polymorphism in compounds.
► Spectroscopy methods: Here these interactions have been studied via NMR, FT-IR and single crystal X-ray diffractions.
► Calculations: The calculations were performed using the Gaussian 03 package.